New Lathe

Advert

New Replies

Report Bug

Help/FAQs

New Lathe

This topic has 46 replies, 22 voices, and was last updated 1 November 2013 at 00:13 by Dave Harding 1.

Viewing 25 posts - 1 through 25 (of 47 total)

1 2 →

Author

Posts
25 October 2013 at 21:27 #133673
Dave Harding 1
Participant
@daveharding1
I have purchased my first lathe a 9×20 metric jobby.

I understood a amount of fettling was required to these Chinese lathes. But I am surprised at the build quality. I am all ready having to fix stuff on it to make it work

At the moment I am struggling it is cutting a taper when I try to take straight cuts I am a novice and I am struggling to undersatand why it is doing this.
Advert

25 October 2013 at 21:27 #6930
Dave Harding 1
Participant
@daveharding1
9×20
25 October 2013 at 21:39 #133675
jason udall
Participant
@jasonudall57142
Well turning taper when you expect parallel.
Causes.
Metal moving away from tool..
Or less likely machine is not “straight” ie ways of machine donot share the alignment of the spindle ( center of rotation of the bar you are turning)..
A tailstock center will help with the first…as will reducing the cutting force..sharp and on center height and shallower cuts..

tk
25 October 2013 at 21:53 #133678
Russell Eberhardt
Participant
@russelleberhardt48058
Dave,

It might be a good idea to give us a bit more information as there are a lot of possible causes. Are you turning the part between centres or held in the chuck? What are the dimensions of the part? How much taper is there?

Any other information that you think might be relevant?

Russell.
25 October 2013 at 22:28 #133694
Martin Cottrell
Participant
@martincottrell21329
Hi David,

Even expensive lathes will turn a taper if not set up and levelled correctly. There are loads of books, forum postings, YouTube videos etc on setting up a new lathe and a couple of hours spent in that direction will give you a good basis to start from. The lathe may look like a substantial lump of iron but it is surprising how much twist you can induce into the bed by not bolting to a flat surface or uneven tightening of the bolts on a surface with some degree of "give" such as a wooden work bench.

As Jason pointed out, other causes could be insufficient support of the work allowing it to flex away from the tool when cutting, this effect reduces as the tool gets closer to the chuck giving you a taper which would narrow towards the chuck. Also if using the top slide to cut, the top slide may not be running truly parallel to the lathe axis. It would help to narrow down the likely cause of your problem if you could describe the machining set up you are using and also the degree of taper you are measuring and whether it is narrower towards the chuck or towards the tail stock end.

Dont despair, with a bit of careful setting up and using sharp, correctly set tools and good work holding techniques you should be able to produce accurate work with your lathe. Also don't be afraid to ask questions however daft you think they may be! There are a lot of people on here, myself included, who have started as novices with no engineering background and know how daunting it can be to start with but who soon start producing excellent results with a bit of friendly encouragement!

Regards, Martin
26 October 2013 at 00:41 #133702
Dave Harding 1
Participant
@daveharding1
Thanks for the replies.

The taper is narrower at the tail stock and increases as you get nearer the chuck

I initially used a piece of 1/2" aluminium bar 4" long secured in the chuck I centred the cutter then faced the work piece no dimple so I then used the top slide to make a 1" long straight cut. I did this in small passes then removed the piece and miked it there was a definite taper.

I tried again with a piece of 5/8" bar stock 4" long secured I the chuck faced it then started to turn the bar stock I ended up with a taper a smaller diameter at the tail stock and larger at the chuck its not a huge amount but as I bought the lathe to make small machine parts that have to be a exact measurement if I can not sort this then the lathe is no use to me.

I have had it a month the speed control knob proved to be useless after two days I replaced it with one from a needle valve we use at work.

Adjusting the cross slide is a pain to morrow I am going to modify it so it is more user friendly.

None of the verniers on any of the adjusting wheely things are accurate.

Up to now I am not very happy with this lathe. I have lots of projects I want to get under way but there is no way I would tackle any of them with this lathe.
26 October 2013 at 05:23 #133707
Thor 🇳🇴
Participant
@thor
Hi Dave,

you say you "used the top slide to make a 1" long straight cut. ". If the top slide is not exactly parallel to the center line of the lathe, it will turn a taper. If I am to turn a short taper I set the top slide over and use it to cut the taper. For turning a straight cylinder I would move the carriage along the bedways. As others have said, your lathe should be placed on a level bench (i.e. no twist in the bed) to turn straight.

Regards

Thor
26 October 2013 at 09:15 #133716
Sub Mandrel
Participant
@submandrel
Hi Dave, how great is the taper? If the tool is not perfectly sharp and the cuts very light 1/2" or 5/8" aluminium will flex.

THIS CALCULATOR when fed with your conditions shows a flex of over 0.001" for a 4-lbf cutting force. That's 2-thou of taper, and your cutting force could well be more than that.

If your errors are of this order, use tailstock support and make sure all your slides are well adjusted before suspecting the basic accuracy of the lathe.

Neil
26 October 2013 at 10:05 #133721
Gray62
Participant
@gray62
Hi Dave,

Where in the country/world are you? There may be someone local that can help you get your lathe set up correctly, or maybe a local club.

What model of lathe do you have, you said a 9×20 but there are many variants that fall into that category.

CB.
26 October 2013 at 10:13 #133722
JasonB
Moderator
@jasonb
Neil if the work is flexing away from the tool that does not explain why its a smaller dia at teh tailstock end, flex would give the opposite result.

Seems to be an alinement issue
26 October 2013 at 10:17 #133723
Ady1
Participant
@ady1
Yahoo used to have some good lathe groups
26 October 2013 at 11:29 #133729
Dave Harding 1
Participant
@daveharding1
I have tried umpteen times to access yahoo groups give it up as a bad job.

The lathe is bolted down onto a bench it is level.

I used a 4" long piece od 5/8" steel bar this time faced it off. Then started taking small 1" long cuts. I measured the work piece its actually tapered from the chuck to the tail stock. I got it the wrong way around Its .5630 at the chuck and .5480 at the tail stock.

I think I might of sussed it I assumed the vernier on the cross slide would be accurate and used the graduations to set it up what I thought would be square on to the work but after using a tape measure to check its not. Looks like I am going to have use a steel rule when I am setting it up to carry out any work on it. hmmmmmmmmmmm.
26 October 2013 at 12:02 #133732
JasonB
Moderator
@jasonb
Right if its bigger away from the chuck there are a few likely candidates.

If you have 4" of bar sticking out the chuck the end will flex away from the tool as neil mentioned and produce a taper. If you only want to turn 1" then have 1 1 /8" sticking out the chuck. If you want to turn the whole 4" then on that dia you will need tailstock support ( make sure tailstock is on teh same axis as spindle)

If you are still using the topslide to turn your 1" length then don't use the carrage instead. If you must use the topslide then it wants clocking true using a DTI or dial gauge, tape measure will not be accurste.

Also you say the bench is level or the lathe, a builders level is not really the most accurate level, an engineers one used along and across the bed at various points will show any slight twist

J
26 October 2013 at 12:05 #133733
John Stevenson 1
Participant
@johnstevenson1
Posted by Dave Harding 1 on 26/10/2013 11:29:34:

I thought would be square on to the work but after using a tape measure to check its not. Looks like I am going to have use a steel rule when I am setting it up to carry out any work on it. hmmmmmmmmmmm.

You are not using this machine for dressmaking are you ?
26 October 2013 at 12:58 #133735
Sub Mandrel
Participant
@submandrel
Hi Dave,

Don't despair. Your lathe can probably do all you want of it, but as you build your skills you'll find out that 'level','square' and 'parallel' demand more of our skills in engineering than in everyday life!

I misread '"increases as you get nearer the chuck" but it seems it does get bigger near the tailstock.

Jason is right, don't rely on the graduations to set the topslide – you need to judge the graduations to a thousandth of an inch and even if they are accurate you can't do that by eye. You may be able to set it square using a GOOD engineers square if they are ground accurately all over.

Even so. it's normal to do nearly all cutting suing the cross slide (for facing across the lathe) and saddle movements. the top slide is usually reserved for tapers (which are often set by trial and error or 'cut and fit&#39 or for moving the tool by accurate distances (e.g. you want to turn a set of carefully spaced grooves).

The old masters could turn anything to a perfect fit with a steel rule and some calipers. Us mortals greatly benefit from some more advanced equipment – a decent digital vernier is the cheapest way to start working accurately, but in time you will probably want a DTI and a micrometer as well.

If you aren't sure on anything, don't be afraid to ask – none of us knew when we started either. You've found a good place to seek advice.

Regards

Neil
26 October 2013 at 13:58 #133738
Russell Eberhardt
Participant
@russelleberhardt48058
I presume that your lathe is one like this They were marketed in the UK under the Champion and Warco brands.

I had one of these lathes for a while and it was capable of turning parallel to within a thousandth of an inch over a distance of six or eight inches whan properly set up. There is no reason why yours shouldn't be the same.

As others have said, you must apply the feed for cutting parallel using the saddle traverse wheel (the big wheel on the left of the saddle). The topslide cannot be set accurately enough without a dial gauge or similar.

Don't worry about the lathe being "level". This is a rather confusing term. What is really meant is that the bed shouldn't be twisted by bolting it down to a non-flat surface but that won't cause anything like as much taper as you are getting nor will deflection of the work.

Have another go using the saddle traverse and see how you get on.

You might find it useful to get a copy of this book but continue asking questions here and let us know how you get on.

Russell.
26 October 2013 at 17:05 #133749
michael howarth 1
Participant
@michaelhowarth1
Dave ….I have got one of those lathes and I had a devil of a job getting it to turn parallel, but at no time did I experience the amount of deviation that you are experiencing. From what you have written it seems that you are using the top slide to turn and if it is not set up absolutely dead square to the lathe axis then you will get a signiificant taper….in fact I rarely use the top slide for anything other than taper turning. I would go along with the comments made by Russell, Jason and Neil above…..use the saddle traverse for normal turning or try it on autofeed.
26 October 2013 at 17:36 #133755
Steve Withnell
Participant
@stevewithnell34426
It will get bigger nearer the tailstock. Even if you have your lathe set up perfectly. This is because the aluminium bar will move away from the tool at the tailstock end if it is unsupported. My lathe is similar to yours and the handbook describes mounting a 50mm steel bar 100mm long and using that as a test piece to set up the lathe.

Even with a big chunk of steel you only take the very lightest of cuts.

Harold Hall has a good book – "Lathework – a Complete Course" Really easy to follow and its a cheap book too.

Steve
26 October 2013 at 17:48 #133756
Russell Eberhardt
Participant
@russelleberhardt48058
Posted by Steve Withnell on 26/10/2013 17:36:16:

It will get bigger nearer the tailstock. Even if you have your lathe set up perfectly. This is because the aluminium bar will move away from the tool at the tailstock end if it is unsupported.

Yes but not nearly as much taper as he's getting and his taper is the other way round.

Russell.
26 October 2013 at 19:01 #133760
Dave Harding 1
Participant
@daveharding1
Its not protruding 4". Its a 4" piece of bar stock only 1 1/2" inch was protruding from the chuck.

I then repeated the exercise with a piece of 5/8" steel bar. Using the saddle traverse its still cutting a taper.

I have ordered a copy of Lathework by Harold Hall.

I have a piece of 7/8" silver steel round bar I will have another go with that tomorrow if I can not sort this out the lathe is no good to me.
26 October 2013 at 19:06 #133761
KWIL
Participant
@kwil
You have not said whether or not you have tried cutting just using the carriage along the bed (ie no change of topslide)
26 October 2013 at 19:18 #133764
Sub Mandrel
Participant
@submandrel
Hi Dave,

Check that all the slideway gibs are reasonably tight and well lubricated. Those measurements (24 thou over 1 1/2&quot are a LONG way out. Put the longest bar you have in the chuck, with as much sticking out as you can get while supporting it fully by the chuck jaws. If you can get 6" sticking out the error on each side should be over 1mm – this will be easily visible if you sight the bed of the lathe along the edge of the bar, looking down from above. Rotate the chuck by hand just in case the chuck hasn't held the bar very accurately.

If you can't see such an error in the bar, the problem is unlikely to be alignment. If it is that far out that you can see such a gross error, then look at how the headstock is fixed to the lathe bed and check that the spindle bearings are properly adjusted.

Neil
26 October 2013 at 19:48 #133766
Steve Withnell
Participant
@stevewithnell34426
Dave – In the old days, a turner would be apprenticed for 7 years, so if it takes you 3 or 4 weeks to get on top of this, well thats not bad progress.

I've no idea of your background, so can't really judge the issue you are facing. What make and model of machine is it that you bought, who did you buy it from? What measuring equipment are you using?

I can scan and post the setup for my lathe (10×22 chinese) if that would be helpful to you.

Steve
27 October 2013 at 21:30 #133904
Dave Harding 1
Participant
@daveharding1
I took the thing to bits to day measured every thing then reassembled it.

I put a 7/8" piece of silver steel bar stock 12" in the chuck and supported the other end with the tail stock and spun the work very slowly I then checked the rotation against the bed it looked to me like it was not turning true not by a massive amount but I don't know if this is normal.

I then put a 4" inch long piece of 1" bar stock in the chuck. I put approx. 2" in the chuck and left 2" sticking out.

I centred the tools faced the bar stock of. I then made a cut with a parting tool about 1" from the end of the bar.

I locked everything down and used the saddle traverse to take metal of I ended up with starting at the tail stock and measuring to wards the chuck.

.9340 .9330 .9320 .9335 .9310 is that normal for this type of lathe or should I be able to better this.
27 October 2013 at 21:41 #133908
John Stevenson 1
Participant
@johnstevenson1
Firstly was this just one pass to remove the 60 odd thou or so ? no final clean up pass ?

Why would you use a parting tool ?

With all due respect I think you need to take things steady and have a read up of that book you have bought or watch some training videos on you tube then work at your problem logically.

From the figures given which aren't bad I'm sure they can be improved on with a little more experience.
Author

Posts